The invention relates to a digital real-time video image processing device according to the principle of non-linear manipulation of the brightness distribution of television pictures by means of matching the brightness distribution (histogram) to a prescribed function. Such image processing devices serve for improving the image contrast and, thus, the image quality.
The calculation of the allocation of gray scale values from the histogram is generally known from the literature. The reallocation of the brightness values is calculated by means of mathematical operations in a mass computer. This method is very involved and does not supply the enhanced images in real time.
A method is disclosed in the publication SPEI/OSA Vol. 74 (1976) "Image Processing", pages 120 through 125, in which the compensation of the histogram is directly gained by means of an electronic circuit. The only thing specified in the publication is the manner of functioning of this circuit and an indication of the manner of realizing such an arrangement is not given. The only thing shown is the required outlay for components and this is very extensive in this case.
The non-linear manipulation of the brightness distribution (histogram) of video images serves for enhancing the contrast. It is applied to every image point. A histogram indicates the frequency of the occurrence of brightness values of image points of a video image. A non-uniform distribution derives in most cases. New brightness values are computationally assigned to the individual brightness levels for the purpose of boosting contrast until a prescribed, for example, horizontal progression of the histogram derives. In so doing, the frequently occurring brightness stages appear spread, so that the contrast between these stages is increased. A spread of the used brightness can also thereby derive, since the brightness range is better exploited.